1. Field of the Invention
The present invention relates to a data transmission method and apparatus for converting eight-bit word string data representing signal information, such as video signal information, converted from ten-bit word string data, into ten-bit word string data including synchronous word data, and for transmitting the converted data to a transmission channel.
2. Description of the Related Art
As one of the means for transmitting digital data indicating various signal information, such as video signal information, an optical transmission system is proposed in which digital data is converted into a light signal, and is transmitted through a transmission channel, which is formed of optical fiber. Digital data handled in this type of optical transmission system is converted into serial data having a bit rate of, for example, a few hundreds of Mbps to one Gbps.
Digital data handled in one of the optical transmission systems, e.g., in a fiber channel system, is converted in the following manner. At the transmitting side, eight-bit word string data (eight bits forms one word) is converted into ten-bit word string data (ten bits forms one word), i.e., 8B-10B conversion is performed. Further, parallel-to-serial conversion is performed on the resulting ten-bit word string data, thereby obtaining serial data. At the receiving side, serial-to-parallel conversion is performed on the received serial data. Then, the ten-bit word string data is converted into the original eight-bit word string data, i.e., 10B-8B conversion is conducted.
The digital data to be transmitted as the ten-bit word string data through the transmission channel, which is formed of an optical fiber, in the fiber channel system is compliant with the data format such as the one shown in FIG. 6. In this data format, a packet is formed as the smallest unit, which is referred to as a xe2x80x9cframexe2x80x9d. The entire frame shown in FIG. 6 has 2148 bytes, and is formed of a 4-byte frame start field, a 24-byte frame header field, a 64-byte optional header field, a 2048-byte payload field, a 4-byte error check field, and a 4-byte frame end field. Among these frame fields, the 2048-byte payload field stores ten-bit word string data representing signal information. More specifically, at the transmitting side, a plurality of frames, each storing the ten-bit word data having a maximum amount of 2048 bytes in the payload field, are formed, and are sequentially transmitted. Upon receiving the frames, the receiving side extracts the ten-bit word string data from the payload fields of the individual frames.
In the above-described ten-bit word string data, the number of ones may be greater than the number of zeros, or the number of zeros may be greater than the number of ones, or the number of ones and the number of zeros may be equal. This can be represented by the concept of xe2x80x9crunning disparity (RD)xe2x80x9d. When the number of ones is greater than the number of zeros, RD is positive. When the number of zeros is larger than the number of ones, RD is negative. When the number of ones and the number of zeros are equal, RD is neutral. The word data having a greater number of ones than zeros is referred to as the xe2x80x9cword data having a positive RDxe2x80x9d. The word data having a greater number of zeros than ones is referred to as the xe2x80x9cword data having a negative RDxe2x80x9d. The word data having the same number of ones and zeros is referred to as the xe2x80x9cword data having a neutral RD (neutral word data)xe2x80x9d.
In conducting 10B-8B conversion on the received ten-bit word string data, it is necessary for the receiving side to correctly identify the individual ten-bit word string data. Accordingly, at the transmitting side, synchronous word data is suitably inserted in the ten-bit word string data to be transmitted as serial data. Although the synchronous word data is also ten-bit word data, it has a specific code, which is not used for the regular ten-bit word data indicating information to be transmitted. If the RD of the word data positioned immediately before the synchronous word data to be inserted is negative, the RD of the synchronous word data is determined to be positive. Conversely, if the RD of the word data immediately before the synchronous word data to be inserted is positive, the RD of the synchronous word data is determined to be negative.
The synchronous word data may be ten-bit word data DS(10), whose code name is referred to as xe2x80x9cK28.5xe2x80x9d. FIG. 7 illustrates such ten-bit word data DS(10). When the CRD, which is the RD of the previous word data, is negative (xe2x88x92), the word data DS(10) results in xe2x80x9c001111 1010xe2x80x9d having a positive RD. In contrast, when the CRD, which is the RD of the previous word data, is positive, the word data DS(10) results in xe2x80x9c110000 0101xe2x80x9d having a negative RD (hereinafter xe2x80x9c001111 1010xe2x80x9d is referred to as xe2x80x9c+K28.5xe2x80x9d, while xe2x80x9c110000 0101xe2x80x9d is referred to as xe2x80x9cK28.5xe2x80x9d).
It is now assumed that the ten-bit word string data to be transmitted designates video signal information. To enhance the transmission efficiency, it is desired that the greatest possible number of ten-bit word string data be stored in the payload field of each frame. Thus, at the transmitting side, ten-bit word string data corresponding to many horizontal periods of the video signal are stored in the payload field of each frame. Meanwhile, to establish horizontal synchronization in performing data processing by the receiving side, it is desired that synchronous word data be inserted in the ten-bit word string data corresponding to every horizontal period of the video signal.
To fulfil the above-mentioned function of the synchronous data, it is now assumed that the synchronous data is inserted as +K28.5 or xe2x88x92K28.5 according to whether the RD of the previous word data is negative or positive, as stated above.
As discussed above, at the transmitting side of, for example, the fiber channel system, many frames are formed in which ten-bit word string data, added with the word data DS(10) as the synchronous word data, are stored in the payload fields. The frames are then sequentially transmitted. Upon receiving the frames, the receiving side extracts the ten-bit word string data from the payload field of each frame and detects the synchronous word data, generally, as follows, before processing the ten-bit word string data. Only the word data DS(10) having a positive RD, i.e., +K28.5, is detected as the synchronous data. Alternatively, only the word data DS(10) having a negative RD, i.e., xe2x88x92K28.5, is detected as the synchronous data. This is because a predetermined restriction is imposed on the addition of the synchronous word data to the ten-bit word string data. Due to this restriction, it is sufficient for the receiving side to detect only +K28.5 or xe2x88x92K28.5 of the synchronous word data.
However, if only the word data DS(10) having a positive RD, i.e., +K28.5, or only the word data DS(10) having a negative RD, i.e., xe2x88x92K28.5, is detected, the following problem is caused when the receiving side performs data processing under the following situation. That is, to fulfil the function of the synchronous word data, as stated above, the word data DS(10) having a positive RD, i.e., +K28.5, or the word data DS(10) having a negative RD, i.e., xe2x88x92K28.5, is inserted in the ten-bit word string data corresponding to every horizontal period of the video signal according to whether the RD of the previous word data is negative or positive.
More specifically, if only +K28.5 or xe2x88x92K28.5 is detected as synchronous data at the receiving side, the synchronous word data cannot be detected for the ten-bit word string data corresponding to every horizontal period of the video signal in processing the ten-bit word string data. As a result, in reproducing the video signal information represented by the ten-bit word string data, correct horizontal synchronization may not be reliably established.
Consequently, in transmitting digital data representing various signal information, such as video signal information, accompanied by the 8B-10B conversion and the addition of the synchronous word data at the transmitting side, and the detection of the synchronous word data and the 10B-8B conversion at the receiving side, the use of integrated circuit (IC) devices for processing digital data in, for example, the fiber channel system, becomes difficult. By using the above types of IC devices, the word data DS(10) having a positive RD, i.e., +K28.5, or the word data DS(10) having a negative RD, i.e., xe2x88x92K28.5, is inserted as the synchronous word data in the ten-bit word string data corresponding to every horizontal period of a signal according to whether the RD of the previous word data is negative or positive. Thus, the above-described problems occur in detecting the synchronous word data from the ten-bit word string data at the receiving side.
Accordingly, in view of the above background, it is an object of the present invention to provide a data transmission method and apparatus in which, after transmitting ten-bit word string data including synchronous word data, converted from eight-bit word string data representing signal information, such as video signal information, data synchronization, which is required for reproducing the signal information, such as converting the ten-bit word string data into the eight-bit word string data, is reliably established at the receiving side even if only the synchronous word data having a positive RD or only the synchronous word data having a negative RD is detected at the receiving side.
In order to achieve the above object, according to one aspect of the present invention, there is provided a data transmission method including: a receiving step of receiving eight-bit word string data indicating signal information; an insertion step of inserting an additional word data group including specific synchronous word data and at least one item of auxiliary word data, each data having eight bits and a predetermined code, between words of the eight-bit word string data in accordance with a predetermined timing signal; a conversion step of converting the eight-bit word string data provided with the additional word data group into ten-bit word string data; a forming step of forming composite ten-bit word string data including the additional word data group containing ten-bit synchronous word data which is converted from the specific synchronous word data; and a transmission step of transmitting the composite ten-bit word string data. In the above-described insertion step, the additional word data group is selected so that the RD of the ten-bit synchronous word data contained in the additional word data group of the composite ten-bit synchronous word data is consistently positive or negative.
According to another aspect of the present invention, there is provided a data transmission apparatus including a digital data forming unit for forming eight-bit word string data indicating signal information. A ten-bit word string data forming unit inserts an additional word data group including specific synchronous word data and at least one item of auxiliary word data, each data having eight bits and a predetermined code, between words of the eight-bit word string data in accordance with a predetermined timing signal, and converts the eight-bit word string data provided with the additional word data group into ten-bit word string data, thereby forming composite ten-bit word string data including the additional word data group containing ten-bit synchronous word data which is converted from the specific synchronous word data. A data transmitting unit transmits the composite ten-bit word string data. The ten-bit word string data forming unit inserts the additional word data group between the words of the eight-bit word string data so that the RD of the ten-bit synchronous word data contained in the additional word data group of the composite ten-bit synchronous word data is consistently positive or negative.
According to the aforementioned data transmission method and data transmission apparatus, as discussed above, the composite ten-bit word string data to be transmitted includes ten-bit synchronous word data constantly having a positive or negative RD. Such ten-bit synchronous word data is set to be the word data DS(10) having a positive RD, i.e., +K28.5, or the word data DS(10) having a negative RD, i.e., xe2x88x92K28.5. It is determined whether the ten-bit synchronous word data contained in the composite ten-bit word string data constantly exhibits positive or negative according to which RD, i.e., positive or negative, of the synchronous word data the receiving side detects.
The composite ten-bit word string data transmitted as described above can be correctly and suitably detected as synchronous word data required for converting from the ten-bit word string data into the eight-bit word string data by the receiving side. It is thus possible to reliably establish data synchronization required for reproducing signal information represented by the received composite ten-bit word string data by the receiving side.
According to the aforementioned data transmission method and data transmission apparatus, integrated circuit (IC) devices provided for digital data processing in, for example, a fiber channel system, can be effectively utilized.
The additional word data group contained in the composite ten-bit word string data may be formed of four, three, or two word data.
It is now assumed that the additional word data group contained in the composite ten-bit word string data has four word data. When the RD of ten-bit word data positioned immediately before the additional word data group is positive, the additional word data group of the composite ten-bit word string data may include ten-bit word data having a negative RD, ten-bit word data having a neutral RD, ten-bit synchronous word data having a positive RD, and another ten-bit word data, or may include the ten-bit word data having a negative RD, the ten-bit synchronous word data having a positive RD, and another ten-bit word data. Conversely, when the RD of ten-bit word data positioned immediately before the additional word data group is negative, the additional word data group of the composite ten-bit word string data may include ten-bit word data having a neutral RD, another ten-bit word data having a neutral RD, the ten-bit synchronous word data having a positive RD, and another ten-bit word data, or may include the ten-bit word data having a neutral RD, the ten-bit synchronous word data having a positive RD, and another ten-bit word data.
Alternatively, when the RD of ten-bit word data positioned immediately before the additional word data group is negative, the additional word data group of the composite ten-bit word string data may include ten-bit word data having a positive RD, ten-bit word data having a neutral RD, ten-bit synchronous word data having a negative RD, and another ten-bit word data, or may include the ten-bit word data having a positive RD, the ten-bit synchronous word data having a negative RD, and another ten-bit word data. Conversely, when the RD of ten-bit word data positioned immediately before the additional word data group is positive, the additional word data group of the composite ten-bit word string data may include ten-bit word data having a neutral RD, another ten-bit word data having a neutral RD, the ten-bit synchronous word data having a negative RD, and another ten-bit word data, or may include the ten-bit word data having a neutral RD, the ten-bit synchronous word data having a negative RD, and another ten-bit word data.
It is now assumed that the additional word data group contained in the composite ten-bit word string data is formed of three word data. When the RD of ten-bit word data positioned immediately before the additional word data group is positive, the additional word data group of the composite ten-bit word string data may include ten-bit word data having a negative RD, ten-bit word data having a neutral RD, and ten-bit synchronous word data having a positive RD, or may include the ten-bit word data having a negative RD and the ten-bit synchronous word data having a positive RD. Conversely, when the RD of ten-bit word data positioned immediately before the additional word data group is negative, the additional word data group of the composite ten-bit word string data may include ten-bit word data having a neutral RD, another ten-bit word data having a neutral RD, and the ten-bit synchronous word data having a positive RD, or may include the ten-bit word data having a neutral RD and the ten-bit synchronous word data having a positive RD.
Alternatively, when the RD of ten-bit word data positioned immediately before the additional word data group is negative, the additional word data group of the composite ten-bit word string data may include ten-bit word data having a positive RD, ten-bit word data having a neutral RD, and ten-bit synchronous word data having a negative RD, or may include the ten-bit word data having a positive RD and the ten-bit synchronous word data having a negative RD. Conversely, when the RD of ten-bit word data positioned immediately before the additional word data group is positive, the additional word data group of the composite ten-bit word string data may include ten-bit word data having a neutral RD, another ten-bit word data having a neutral RD, and the ten-bit synchronous word data having a negative RD, or may include the ten-bit word data having a neutral RD and the ten-bit synchronous word data having a negative RD.
It is now assumed that the additional word data group contained in the composite ten-bit word string data is formed of two word data. When the RD of ten-bit word data positioned immediately before the additional word data group is positive, the additional word data group of the composite ten-bit word string data may include ten-bit word data having a negative RD and ten-bit synchronous word data having a positive RD. Conversely, when the RD of ten-bit word data positioned immediately before the additional word data group is negative, the additional word data group of the composite ten-bit word string data may include ten-bit word data having a neutral RD and the ten-bit synchronous word data having a positive RD.
Alternatively, when the RD of ten-bit word data positioned immediately before the additional word data group is negative, the additional word data group of the composite ten-bit word string data may include ten-bit word data having a positive RD and ten-bit synchronous word data having a negative RD. Conversely, when the RD of ten-bit word data positioned immediately before the additional word data group is positive, the additional word data group of the composite ten-bit word string data may include ten-bit word data having a neutral RD and the ten-bit synchronous word data having a negative RD.